Green manure incorporation with nitrogen reduction improves water productivity of spring wheat in arid areas

Water scarcity and high grain yield are the two critical challenges for sustainable agricultural development. An appropriate amount of green manure (GM) incorporation with nitrogen (N) reduction can ensure high and stable crop yields, but it remains unclear whether this approach can enhance soil moisture status and optimize water use characteristics. This study aimed to investigate the effects of different amounts of GM incorporation with N reduction on the grain yield and water use characteristics of wheat. A field experiment was conducted in the arid irrigated area of Northwest China from 2021 to 2023. Seven treatments were established: (i) conventional N application without GM (N100), (ii) 15,000 kg ha −1 GM + 15 % N reduction (M1N85), (iii) 15,000 kg ha −1 GM + 30 % N reduction (M1N70), (iv) 22,500 kg ha −1 GM + 15 % N reduction (M2N85), (v) 22,500 kg ha −1 GM + 30 % N reduction (M2N70), (vi) 30,000 kg ha −1 GM + 15 % N reduction (M3N85), and (vii) 30,000 kg ha −1 GM + 30 % N reduction (M3N70). The results showed that compared with N100, GM incorporation with N reduction had the advantages of increasing soil organic matter (SOM) and total nitrogen (STN) at 0 −120 cm and canopy coverage (CC), root biomass (RB), and dry matter accumulation (DMA) from the anthesis to maturity stage, among which M3N85 had the most significant effect. Meanwhile, this treatment effectively increased soil water storage (SWS) at 0 −120 cm in the three main growth stages (vegetative, concurrent, and reproductive growth stages), reduced soil evaporation (SE) in the three main growth stages, and increased transpiration (T) in the concurrent and reproductive growth stages, finally increasing wheat grain yield (GY) and water productivity (WP) by 28.1 % and 22.7 %, respectively. In addition, structural equation model (SEM) revealed that DMA was the main factor in improving WP. In conclusion, 30,000 kg ha −1 GM + 15 % N reduction could be an effective agricultural strategy to alleviate the contradiction between high wheat yield and water shortage in this region. • Green manure incorporation with nitrogen reduction had the potential to improve wheat GY and WP. • M3N85 increased SWS at 0–120 cm, effectively inhibited SE, promoted effective T, and coordinated ST/ET and T/ET. • M3N85 increased CC, RDW, and DMA of wheat from jointing to maturity. • DMA is the most critical factor to promote wheat water efficient use.